Final answer:
The dromotropic effect refers to the influence on the speed of conduction through the AV junction. Adrenaline and beta-blockers can affect this rate by increasing or decreasing it, respectively. The AV node has the slowest firing rate in the heart conduction system.
Step-by-step explanation:
The drug effect that influences the speed of conduction through the atrioventricular (AV) junction is known as the dromotropic effect. This effect specifically refers to the change in the velocity of electrical conduction in the heart. Drugs that have a dromotropic effect can either slow down or speed up the heart rate by affecting the AV node's conduction properties.
For example, adrenaline can increase the rate of conduction through the AV node, while beta-blockers can slow it down. The atrioventricular node, which is part of the heart conduction system, would have the slowest rate of firing when compared to the atrioventricular bundle, bundle branches, and Purkinje fibers. Drugs that affect both divisions of the autonomic system and can influence heart rate and blood pressure include those that bind to beta-adrenergic receptors.
In case of atropine poisoning, a muscarinic agonist could be used as an antidote to counteract the effects of this anticholinergic drug.